Rename package to satisfy the requirements of the PyPI trusted publisher

The package can still be imported using `django-saml2-auth` after rename,
yet due to PyPI project name not being customizable when using the
pypa/gh-action-pypi-publish@v1 GitHub Action, I had to match the package name
with the project name in PyPI. This will have no impact on the innerworkings
of the package moving forward. I build and tested the package with both names,
and they both can be imported with the same old name. I also updated the Poetry
lock file.